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The present invention relates to internal combustion engines and to fueled motive power units which may, for example, be applied to generate electricity or perform other mechanical work.
Internal combustion engines have been around for over a century and engineers have evolved a number of constructions that optimize one or more of the factors affecting their operation to enhance performance in the various particular functions in which they are employed. The present invention relates generally to piston engines.
In general, a number of factors must be considered in designing a piston engine. Such an engine operates generally by compressing a fuel mixture, igniting the mixture and extracting mechanical energy from the expanding combustion gases by driving the piston with the combustion. The piston, in turn, is mechanically coupled to perform useful work as it moves, e.g., by turning drive wheels of a vehicle, turning the rotor of a generator, moving the tool or work piece holder of an industrial machine, or other such action. The complexity of construction of an internal combustion engine may cover a great range, with different mechanical linkages to effect movement of the pistons, and in four stroke embodiments to coordinate piston travel with movement of valves and other components. Often the efficiency of an engine varies with engine speed, and basic design choices such as the stroke, compression ratio, and the like affect the overall efficiency that may be achieved. These factors may vary both for practical reasons (owing to limitations of carburetion processes, airflow, gearing efficiencies and the like) and for intrinsic or theoretical reasons (owing to thermodynamic limitations related to supply and combustion pressures and temperatures, cycle time and the like).
One construction that has been proposed as a small motor for delivering electric power addresses a number of these factors by combining a piston/cylinder combustion unit with an oscillatory spring mass alternator mechanism. This construction, now conventionally termed midget internal combustion engine (or MICE), employs a piston/cylinder mechanism operated as a conventional two-stroke engine, with the piston carried on a central rod that linearly reciprocates as the piston moves, operating against the force of a spring so that the engine runs in an oscillatory mode without requiring rotating shafts or journals. In one useful integration, the piston rod carries a coil assembly located so that, as the engine runs, the coil is moved back and forth within the field of a magnet secured to the housing, thus generating electrical power.
Such a construction is mechanically simple, and offers the possibility of running at a constant speed range so that the fuel mixture may be accurately adjusted for power or efficiency. The construction may also be scaled quite small to produce portable or emergency drive units for applications such as electrical power generation.
However, in requiring that a spring store and return energy, one faces certain limitations due to the presence of high stresses that become higher with displacement, and may cause a short fatigue life for the spring, thus leading to engine break down; or that limit the achievable stroke or the level of obtainable compression, hence limiting the thermal efficiency of the engine.
Accordingly, it would be desirable to provide an improved engine construction.
It would also be desirable to provide a linear combustion engine construction in which components are subjected to lower stress levels.
It would also be desirable to provide a dependable small engine.
One or more of the foregoing desirable ends are achieved in accordance with the present invention by a piston/cylinder combustion unit having opposed rigidly connected pistons driven in an oscillatory fashion. The pistons are connected to a common shaft and operate out of phase with each other, such that the power stroke of one corresponds to the compression stroke of the other. A mechanical spring acts on the common shaft, storing energy or exerting a restorative force as the shaft is displaced with piston movement. Preferably, the moving shaft carries a coil assembly near a stationary magnet, forming a reciprocating alternator to produce electricity at the oscillatory frequency. In one embodiment, rather than a mechanical spring, the engine employs an electromagnetic spring. For this purpose, the coil itself may act to exert restoring forces. It may, for example, be coupled to an external control system that applies a control a signal to the coil in accordance with piston position and/or phase or direction of travel to create an electromagnetic restoring force of appropriate magnitude. In another or further embodiment, the shaft may carry a first coil that acts as a spring, and a second coil that functions as an alternator to generate power. Different arrangements of magnets, force coils and power coils are possible.